I was told that the Mac engine was really an Echo / Kioritz, but after looking at the one in " Echo on a Funtana" thread, there is definitely a difference, so now doubts are creeping in!

However, the construction of our 21cc engine is also very different to to the 28/32 McCulloch weedies (which I have a few examples of). - they have cantilever cranks and model aircraft type mounting lugs.

I will definitely pull apart my 21 now! - Some people say that the overhung / cantilever crank is stiffer than the double sided type. ( I have my doubts ), but these guys have had a long practical experience on gas engines, and I would hate to argue with any of them.

Whichever answer is true doesn't really matter, but I would say ( from engineering experience ) that the cantilever crank must be supported by more than 1 bearing!! - it certainly will not be rigid without 2 bearings! ( Except perhaps in the case of a double row type ballbearing, or a long needle roller type), - that's improbable though.
You are obviously someone who gets things done quickly, so I would like to hear how you get on and what conclusions you come to.
Good luck. - Will.